Fluid atomizers are well known in the art. Fluid atomizers are used in sprayers to atomize a discrete quantity of liquid being dispensed. The liquid may be stored in bulk form in a reservoir 22. A manual pump or propellant charge may be used to provide motive force for drawing the liquid from the reservoir 22, to the atomizer and spraying through a nozzle. Once the liquid is sprayed through a nozzle is may be dispersed to the atmosphere, directed towards a target surface, etc. Common target surfaces include countertops, fabric, human skin, etc.
However, current atomizers do not always provide a sufficiently small particle size distribution, particularly at relatively low propellant pressures. Relatively low propellant pressures are desirable for safety and conservation of propellant material.
Attempts in the art include U.S. Pat. No. 1,259,582 issued Mar. 19, 1918; U.S. Pat. No. 3,692,245 issued Sep. 19, 1972; U.S. Pat. No. 5,513,798 issued May 7, 1996; US 2005/0001066 published Jan. 6, 2005; US 2008/0067265 published Mar. 20, 2008; SU 1389868 published Apr. 23, 1988; and SU 1176967 published Sep. 7, 1985. Each of these attempts shows a convergent flowpath provided by straight sidewalls.
The straight sidewalls correspond to conventional wisdom that the shorter flow path provided thereby results in less drag. For example see Lefebvre, Atomization and Sprays (copyright 1989), Hemisphere Publishing Company. Page 116 of Lefebvre shows three different nozzle designs. All three nozzles shave straight sidewalls. Lefebvre specifically teachers improving the quality of atomization by including the “minimum area of wetted surface to reduce frictional losses.” Id.
Lefebvre furthers recognizes the problem of trying to achieve desirable flow characteristics at relatively low flow rates, and the efforts to achieve flow at less than 7 MPa. Lefebvre further acknowledges that a major drawback of the simplex atomizer is that flow rate varies with only the square root of pressure differential. Thus doubling flow rate requires a four times increase in pressure. Id at pp. 116-117.
Another problem with atomizers found in the prior art is that to increase or decrease the cone angle of the spray pattern using an atomizer having the straight sidewalls of the prior art requires rebalancing various flow areas, (e.g. swirl chamber diameter, tangential flow area, exit orifice diameter or length/diameter ratio). Using the present invention, one of ordinary skill knowing the desired product delivery characteristics can easily rescale the helix cup to provide new spray characteristics and simply change out the helix cup to a new one. This process improves manufacturing flexibility and reduces cost relative to changing the entire cap, as occurs in the prior art.
It can be seen there is a need for a different approach, and one which allows for desirable spray characteristics at relatively low pressures.